High tensile modulus nonwoven fabric for cleaning printer machines

ABSTRACT

A nonwoven fabric having high tensile modulus suitable for cleaning printer cylinders is formed by hydroentangling a fibrous nonwoven web formed from higher-melting polyester fibers, lower-melting binder fibers and woodpulp fibers and then thermally bonding the fabric.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to nonwoven fabrics for cleaning cylinders of machinery, such as printing machine cylinders.

2. Description of the Related Art

It is known in the art to use nonwoven fabrics to clean the cylinders of printing machines. U.S. Pat. No. 5,974,976 to Gasparrini et al. describes nonwoven cleaning fabrics having reduced air content and the use of such fabrics to clean the cylinders of a printing press. U.S. Patent Application Publication No. 2002/0187307 to Tanaka et al. describes wet-laid sheets for cleaning printer cylinders. The wet-laid sheets contain between about 5 and 50 weight percent binder fibers and are hydroentangled and creped, followed by heating to fuse the binder fibers after creping. Examples of wet-laid sheets include sheets containing at least 50 percent pulp.

In an effort to reduce costs and to reduce the impact printed materials have on the environment; recycled paper is used as a raw material for printing. However, recycled paper produces more lint than new (i.e., non-recycled) paper. The increased amount of paper lint fibers mixes with ink, solvent, and water creating a semi-solid residue on the blanket and impression cylinders of printing machines. Additionally, unacceptable deformation, or necking, due to elongation of the cleaning fabric can occur as the cloth advances during a wash program. The cleaning fabric would also need to have high paper lint pick up and retention, no surface streaking on the cylinders and high solvent desorption for increasing the cleaning rate.

It would be desirable to provide an improved cleaning fabric for cleaning machine cylinders that has high tensile modulus to avoid fabric elongation while having high paper lint pick up and retention, no surface streaking on the cylinders and high solvent desorption for increasing the cleaning rate at a reasonable cost.

BRIEF SUMMARY OF THE INVENTION

In one embodiment this invention is directed to a high strength nonwoven fabric for cleaning cylinders comprising a spunlaced nonwoven fabric comprising between about 5 and 40 weight percent of binder fibers comprising a lower-melting component, between about 25 and 65 weight percent of higher-melting polyester fibers wherein the lower-melting component comprises a polyester copolymer having a lower melting point than the melting point of the higher-melting polyester fibers and between about 35 and 55 weight percent of wood pulp fibers, and wherein the spunlaced fabric is thermally bonded by at least partially softening or melting the sheath component of the binder fibers to provide a thermally bonded spunlaced nonwoven fabric.

DETAILED DESCRIPTION OF THE INVENTION

The terms “nonwoven fabric” and “nonwoven web” as used herein refer to a sheet structure of individual fibers that are positioned in a random manner to form a planar material without an identifiable pattern, as opposed to a knitted or woven fabric.

The term “spunlaced nonwoven fabric” as used herein refers to a nonwoven fabric that is produced by entangling fibers in a fibrous nonwoven web using fluid jets. For example, a spunlaced nonwoven fabric can be prepared by supporting a fibrous web on a porous support such as a mesh screen and hydroentangling the web by passing the supported web underneath water jets, such as in a hydraulic needling process.

The term “machine direction” (abbreviated as MD) is used herein to refer to the direction in which a nonwoven web is produced (e.g. the direction of travel of the supporting surface upon which the fibers are laid down during formation of the nonwoven web). The term “cross direction” (abbreviated as XD) refers to the direction generally perpendicular to the machine direction in the plane of the web.

The term “polyester” as used herein is intended to embrace polymers wherein at least 85% of the recurring units are condensation products of dicarboxylic acids and dihydroxy alcohols with linkages created by formation of ester units. This includes aromatic, aliphatic, saturated, and unsaturated di-acids and di-alcohols. A common example of a polyester is poly(ethylene terephthalate) (PET) that is a condensation product of ethylene glycol and terephthalic acid.

The term “binder fiber” is used herein to refer to fibers that are thermally bondable (i.e. meltable or partially meltable) at a temperature below that of the degradation or melting point of higher melting base fibers that are combined with the binder fibers in a nonwoven web. Binder fibers can be homogeneous or can comprise multiple component fibers. The term “multiple component fiber” as used herein refers to a fiber that is composed of at least two distinct polymeric components that have been spun together to form a single fiber. The at least two polymeric components are arranged in distinct substantially constantly positioned zones across the cross-section of the multiple component fibers, the zones extending substantially continuously along the length of the fibers. Multiple component fibers that are suitable for use as binder fibers include a lower melting polymeric component on at least a portion of the peripheral surface thereof. The lower melting polymeric component has a melting point that is lower than the melting point of higher melting base fibers in the web. The term “bicomponent fiber” is used herein to refer to a multiple component fiber that is made from two distinct polymer components.

The term “staple fibers” means natural fibers or cut lengths from filaments. Typically staple fibers have a length of between about 0.25 and 5.0 inches (0.6 and 15.2 cm).

The present invention relates to thermally bonded spunlaced nonwoven fabrics that are suitable for cleaning cylinders in printing machines or other equipment. The nonwoven fabrics that contain binder fibers are useful in decreasing fabric elongation.

Fibrous webs suitable for preparing spunlaced nonwoven fabrics for use in some embodiments of the present invention comprise between about 5 and 40 weight percent binder fibers that comprise a lower-melting polyester copolymer component, between about 5 and 55 weight percent of higher-melting polyester base fibers and between about 40 and 60 weight percent of woodpulp fibers.

The low-melting polyester copolymer component preferably has a melting point that is at least about 100° C. to 140° C. less than the melting point of the higher-melting polyester base fiber component. A binder fiber suitable for use in the present invention is a bicomponent fiber comprising a poly(ethylene terephthalate)copolymer sheath and a poly(ethylene terephthalate)core. An example of a suitable poly(ethylene terephthalate)copolymer comprises an isophthalate copolymer of poly(ethylene terephthalate).

Base fibers suitable for use include poly(ethylene terephthalate) fibers. In one embodiment, the nonwoven fabric can be made from a blend of polyester-based binder fibers and base fibers. It should be understood that the range of polyester used can be adjusted by varying the relative amounts of base fiber and binder fiber. For example, if the amount of base fiber were about 5%, the amount of binder fiber could be present at the higher end of its range. The base fibers can comprise microfibers (fiber denier less than 1 denier) or hydrophilic polyester fibers for their increased absorbency. For example, between about 5 and 10 weight percent of the fibers in the web can comprise microfibers and/or hydrophilic polyester fibers. Examples of hydrophilic polyester fibers include those that are treated with a hydrophilic finish. One example is Hydrofix® hydrophilic polyester fibers, available from ADVANSA in Germany. Examples of microfibers suitable for use in the present invention include split fibers. Splittable fibers are made by co-spinning two or more distinct polymeric components into multiple component fibers such that the polymeric components form non-interlocking separable segments across the cross-section of the fibers that extend along the length of the fibers. Splittable fiber cross-sections include “chrysanthemum” cross-sections in which alternating polymeric components are petal-shaped and partially overlapped by adjacent segments, side-by-side, segmented pie (wedge-shaped segments), hollow segmented pie, segmented cross, tipped trilobal, and other cross-sections known in the art. Splittable fibers can be incorporated into the fibrous web and split in the hydroentangling step described below.

The nonwoven fabrics of the present invention can be prepared from precursor fibrous webs that are formed using dry-lay techniques, such as one or more carded fibrous layers, one or more air-laid fibrous layers, or a combination thereof. Methods for preparing air-laid webs and carded webs are well known in the art. For example, air-laid webs can be made according to U.S. Pat. No. 3,797,074 to Zafiroglu or by using a Rando Webber manufactured by the Rando Machine Corporation and disclosed in U.S. Pat. Nos. 2,451,915; 2,700,188; 2,703,441; and 2,890,497, the entire contents of which are incorporated herein by reference. Staple fibers having a fiber length between about 30 and 75 mm and fiber denier between about 1 and 15 are generally preferred for preparing carded nonwoven webs. Staple fibers having a fiber length between about 12.7 mm and 25.4 mm and fiber denier between about 0.9 and 4 are generally preferred for preparing air-laid nonwoven webs. The deniers of the binder and base fibers are preferably closely matched for better processability. The base fibers and binder fibers can be admixed in the web during formation in carding, and the like, or by conventional textile blending techniques followed by carding the blended fibers. Alternately, a blend of fibers may be dispersed in an air stream and collected on a foraminous means in an air-laying process. Alternately, individual webs comprising binder fibers and/or base fibers can be layered followed by hydroentangling the combined layers to form a spunlaced nonwoven fabric that has one side richer in the binder fiber than the other side. For example, a web consisting of binder fibers can be layered with a web consisting of base fibers and then hydroentangled. Alternately, one or more of the layers can comprise a blend of binder and base fibers, wherein one of the outer layers has a higher weight percent of binder fibers than the other outer layer. In another embodiment, a sandwiched 3-layer structure can be formed by laying down webs in the configuration binder fiber web/base fiber web/binder fiber web, wherein the binder fiber webs can include binder fibers or a blend of binder and base fibers and the base fiber web can include of base fibers or a blend of binder and base fibers wherein one or both of the binder fiber layers has a higher weight percent of binder fibers than the base fiber layer. The web can then be hydroentanged to form a spunlaced nonwoven fabric that has one or two binder-fiber rich sides. It should be understood that at least one layer of wood pulp fibers is included in the embodiments described above. Fibrous nonwoven webs having a basis weight between about 50 and 120 g/m², preferably between about 60 and 110 g/m² are suitable for use; however the basis weight can be varied to the extent necessary to develop the desired properties.

Carded webs generally have fibers oriented substantially in the machine direction whereas the fibers in air-laid webs are substantially randomly oriented. Carded webs can be cross-lapped to improve the balance of machine direction and cross direction properties. It is often preferred that the machine and cross direction properties of a nonwoven fabric be balanced, however in one embodiment of the present invention, the nonwoven fabric is prepared from a carded web in which the fibers are substantially oriented in the machine direction.

After forming a fibrous web comprising base fibers and binder fibers, the web is hydroentangled. The hydroentangling (or hydraulic needling) process for producing spunlaced nonwoven fabrics is well known in the art. In the hydroentangling process, the fibrous web is positioned on a screen or other type of apertured support and subjected to a series of high-pressure water jets that cause entangling of the fibers to form a spunlaced nonwoven fabric. Conventional hydraulic needling processes are described in U.S. Pat. No. 3,485,706, to Evans and U.S. Pat. No. 4,891,262 to Nakamae et al., the entire contents of which are incorporated herein by reference. The support member can be porous, such as a metal or plastic belt or screen that is woven from round or other shaped strands, monofilaments or yarns, or a perforated plate. The hydroentangled fabric can be apertured or non-apertured, depending on selection of the support member, as is known in the art. When apertured, the range of aperture size can be from about 13 to 24 mesh. Further, the fabric can be patterned or unpatterned.

After the fibrous web has been hydroentangled, the resulting spunlaced nonwoven fabric is thermally bonded. Thermal bonding conditions are selected such that the lower-melting binder fiber component (e.g. sheath for sheath-core binder fibers) softens or melts but the higher-melting base fiber and the core component of the binder fiber do not melt and retain their fibrous structure. The bonding conditions should be selected such that the final fabric has the desired strength properties. The spunlaced nonwoven fabric can be wound up and thermally bonded at a later time in a separate process. Alternately, thermal bonding can be conducted in-line immediately after hydroentanglement, such as in a heated air dryer. In such a process, excess water can be removed from the spunlaced nonwoven fabric, such as by a vacuum dewatering system or squeeze rolls, prior to passing the fabric through the dryer. In one embodiment, the spunlaced nonwoven fabric is thermally bonded in a through-air dryer in which a heated gas, generally air, is passed through the fabric. The gas is heated to a temperature sufficient to soften or melt the low-melting component of the binder fibers without softening or melting the base fibers to bond the binder and matrix fibers at their crossover points. Through-air bonding generally results in substantially uniform bonding across the width and through the thickness of the fabric, as opposed to surface bonding only. Through-air bonders generally include a perforated drum, which receives the fabric, and a hood surrounding the perforated drum. The heated gas is directed from the hood, through the spunlaced nonwoven fabric, and into the perforated drum. The residence time in the through-air bonder and the temperature of the heated gas is selected to both dry the fabric, if it is wet, and to provide the desired degree of thermal bonding. One or more through-air dryers can be used in series to achieve the desired degree of bonding. It has been found that when the base fibers are poly(ethylene terephthalate) fibers having a melting point of about 250-260° C. and the binder fibers are sheath/core fibers comprising a sheath of low-melting isophthalate copolymer of poly(ethylene terephthalate) having a melting point of about 100-120° C. and a poly(ethylene terephthalate) core, that a bonding air temperature of about 180° C. (fabric temperature of about 130-150° C.) and a residence time between about 8 and 12 seconds in the dryer provides a suitable fabric. The fabric can be thermally bonded in-line immediately after it has been hydroentangled or thermally bonded at later time.

The thermally bonded nonwoven fabric can optionally be calendered. Room temperature calendering can be used to reduce the thickness of the fabric. This allows a longer fabric length to be wound on a core to provide a desired roll thickness when used as a printer cleaning fabric, as described in U.S. Pat. No. 5,974,976 to Gasparrini et al., which is hereby incorporated by reference. It has been found that calendering with unheated rolls at about 25° C. and at a nip pressure of 32-300×10⁻¹ N/cm is suitable for room temperature calendering. Fabric thicknesses up to about 0.70 mm (measured according to EDANA 30.5-99) are suitable for use in the present invention. Although higher thicknesses can be used, it is not desirable from an economic standpoint and also results in less linear meters of fabric for a given cartridge size. Fabric thicknesses between about 0.35 mm and 0.60 mm are generally preferred for the present invention and calendering may be used in order to achieve these thicknesses. Lower thicknesses are preferred in order to get more linear meters of fabric in a cartridge roll so that the cartridge requires changing less often. But if the thickness is too low, ink may seep from one side of the cloth to the other, thereby plugging the water spray bar holes. Higher thicknesses will have the added benefit of additional paper lint fiber retention, but at the expense of less linear meters of fabric in a cartridge and slower solvent release capacity. Alternately, the fabric can be calendered using one or more heated rolls if additional thermal bonding is desired. However, the calendering conditions should be chosen such that the fabric remains sufficiently absorbent to remove ink residue, solvents, or other materials from the surface of the cylinders that are being cleaned. Calendering temperatures in the range of 90-100° C. are generally suitable, with nip pressures in the range of 150 to 250×10⁻¹ N/cm.

The cleaning fabric of the present invention can be employed with conventional printer cylinder cleaning systems, specifically common impression and blanket cylinders of newspaper and commercial web presses. The cleaning fabric is generally wound on a core, such as a hollow cylindrical core, which can be mounted on an unwind position of a printer cylinder cleaning system. A cylinder cleaning system can also include a take-up roll onto which the used portion of the cleaning fabric is wound after it has been used to clean the printer cylinder. Generally a means is provided for positioning the cleaning fabric adjacent a printer cylinder. For example, the cleaning fabric can be placed in contact with a printer cylinder as it is fed past the cylinder.

Generally, a cleaning solvent or solution such as an aliphatic hydrocarbon solvent is applied to the cleaning fabric. The cleaning solution can be applied to the fabric before or after a roll of the cleaning fabric is mounted on the printer cylinder cleaning system. The cleaning fabric can be pre-impregnated with a cleaning solution and packaged for later use, as described in U.S. Pat. No. 5,368,157 to Gasparrini et al. Alternately, the cleaning composition can be applied to the cleaning fabric after mounting on a printer cleaning system such as by using pumps, spray bars, manifold lines, etc. known in the art. The cleaning composition can also be applied with a manual sprayer or other suitable apparatus.

The cleaning fabric is used to remove ink residues, cleaning solvent, lint, and other solid or paste-like matter from the printer cylinders, such as blanket and common impression cylinders. Generally, a pressure pad presses the cleaning fabric into contact with the cylinder during the cleaning process. In addition to dimensional stability and high strength at low elongations, the cleaning fabric must have sufficient absorbency (as provided to a large extent by the wood pulp fibers) to absorb residual solvent, etc. as it is removed from the cylinder surface while under pressure.

Preferred fabrics also demonstrate a high ratio of lubed (wet with surfactant) breaking strength to dry breaking strength as well as high stiffness dry and wet, which indicates less distortion of the fabric under load or dimensional stability when wet with the cleaning solvent. Less distortion leads to fewer tendencies to dislodge the fibers of the fabric.

Test Methods

In the non-limiting examples that follow, the following test methods were employed to determine various reported characteristics and properties. ASTM refers to the American Society of Testing Materials. EDANA refers to the European Disposables and Nonwovens Association for Europe, Middle East and Africa.

Basis Weight is a measure of the mass per unit area of a fabric or sheet and was determined by EDANA 40.3-90 or ASTM D-3776, which is hereby incorporated by reference, and is reported in g/m² (gsm).

Thickness of nonwoven fabrics was measured according to EDANA 30.5-99 or ASTM D1777 and is reported in mm.

Tensile Properties (Grab Breaking Strength and Grab Modulus) were measured on dry samples, according to ASTM D5034-95 that is hereby incorporated by reference. Breaking Strength was reported in units of kg. Modulus was reported herein in units of kN/m.

EXAMPLES Comparative Example A

Comparative Example A was a wood pulp/polyester spunlaced nonwoven fabric that is currently used for cleaning printer machine cylinders and available from E. I. du Pont de Nemours and Company (Wilmington, Del.). The fabric was found to generate an unacceptable amount of XD necking when used to clean printing cylinders.

Example 1

In this example, a blend of polyester bicomponent sheath/core fibers and polyester monocomponent fibers was formed into a spunlaced thermally bonded fabric.

The bicomponent fibers constituted 1.7 dtex 38 mm cut length 15% co-PET/85% PET supplied by ADVANSA, Germany. The bicomponent fibers comprised a sheath formed from a low-melting isophthalate copolymer of poly(ethylene terephthalate) having a melting point of about 11 0C and a core formed from poly(ethylene terephthalate) having a melting point of about 256° C. The polyester monocomponent fibers (1.7 dtex, 38 mm cut length 100% PET, supplied by ADVANSA, Germany) were formed from poly(ethylene terephthalate) and had a melting point of about 256° C. and were blended with the bicomponent fibers to form a fiber blend comprising 15 weight percent of the bicomponent fibers and 85 weight percent of the monocomponent fibers. The total amount of binder fiber as a percentage of the total fabric weight was about 3.6%. The amounts of polyester base fibers and wood pulp are provided in Table 1. The fibers were processed through two high-speed Thibeau cards, one card having the blend of bicomponent and monocomponent fibers and the other card having only monocomponent fibers, to form a carded web, which was then hydraulically needled according to the general process of Evans U.S. Pat. No. 3,485,706. The hydraulically needled sheet was then squeeze rolled with a uniform pressure of 3.0 bars and through-air dried with 2 Fleissner driers at a temperature of 180° C. with a residence time of about 5-6 seconds in each dryer. Fabric properties are reported in Table 1 below.

Properties of the thermally bonded spunlaced nonwoven fabrics are reported below in Table 1. All property measurements were made on 8 (or 10?) samples and averaged.

Example 2

This example was prepared the same way as for Example 1, except that about 7.9% of binder fiber was used and each card processed a blend of bicomponent and monocomponent fibers. The amounts of polyester base fibers and wood pulp are provided in Table 1

Example 3

This example was prepared the same way as for Example 1, except that about 13.1% binder fiber was used in that the bicomponent fibers comprised 1.7 dtex 38 mm cut length 26% co-PET/74% PET, supplied by ADVANSA, Germany. Each card processed a blend of bicomponent and monocomponent fibers. The amounts of polyester base fibers and wood pulp are provided in Table 1.

TABLE 1 Nonwoven Fabric Properties Property Comp Ex A Example 1 Example 2 Example 3 Basis Weight of Fabric 70.90 70.91 71.87 72.03 (g/m²) % Woodpulp 50.60 48.62 47.40 49.47 % PET 49.40 47.78 44.71 37.39 % Binder Fiber 0 3.60 7.89 13.14 Thickness (mm) 0.40 0.41 0.40 0.40 MD Grab Breaking 181 197 188 191 Strength (N) MD Grab Modulus 16 27 28 36 (MPa) MD Grab Load at 5% 50 77 78 92 elongation (N) MD Grab Load at 10% 85 123 117 133 elongation (N) MD Grab Load at 15% 121 166 156 174 elongation (N) XD Grab Breaking 90 93 89 92 Strength (N) XD Grab Modulus 2.0 2.2 1.9 2.7 (MPa) XD Grab Load at 5% 10 11 14 19 elongation (N) XD Grab Load at 10% 13 15 18 25 elongation (N) XD Grab Load at 15% 16 20 23 31 elongation (N) Fabric Necking Left 10 5–6 1–3 0–1 Side (mm) Fabric Necking Right 12–15 8–9 5 1–3 Side (mm)

The presence of the binder fibers in the cleaning fabric provide an increase in MD grab modulus and a decrease in XD necking. All the strength data provided is for dry samples. Lubed samples show similar results. 

1. A high strength nonwoven fabric for cleaning cylinders comprising a spunlaced nonwoven fabric comprising between about 5 and 40 weight percent of binder fibers comprising a lower-melting component, up to about 55 weight percent of higher-melting polyester fibers wherein the lower-melting component comprises a polyester copolymer having a lower melting point than the melting point of the higher-melting polyester fibers and between about 40 and 60 weight percent of woodpulp fibers, and wherein the spunlaced fabric is thermally bonded by at least partially softening or melting the sheath component of the binder fibers to provide a thermally bonded spunlaced nonwoven fabric.
 2. The nonwoven fabric according to claim 1, having a tensile modulus value measured on dry fabric in the machine direction of greater than 25 MPa at 5 to 25% elongation.
 3. The nonwoven fabric according to claim 1 or 2, wherein the binder fibers are bicomponent sheath-core fibers wherein the sheath comprises the lower-melting polyester copolymer component and the core comprises poly(ethylene terephthalate).
 4. The nonwoven fabric according to claim 3, wherein the lower-melting polyester copolymer component is an isophthalate copolymer of poly(ethylene terephthalate).
 5. The nonwoven fabric according to claim 1 or 2, wherein the thermally bonded spunlaced fabric is calendered after thermal bonding.
 6. The nonwoven fabric according to claim 5, wherein the calendering is conducted at about 25° C.
 7. The nonwoven fabric according to claim 1 or 2, wherein the thermally bonded spunlaced fabric is apertured.
 8. A method for cleaning a cylinder having an outer surface comprising the steps of providing the fabric of claim 1 and contacting the outer surface of the cylinder with the fabric.
 9. A method for cleaning a cylinder having an outer surface comprising the steps of providing the fabric of claim 2 and contacting the outer surface of the cylinder with the fabric.
 10. The method according to claim 8 or 9, wherein the cylinder is a component of a printing machine.
 11. The method according to claim 10, wherein the cylinder is an impression cylinder. 